both ebuilds have the gtk and gtk3 use flag. you cant merge them when you activate both. most people want versioned toolkit use-flags like the qt4 and qt5 ones. PLEASE PLEASE PLEASE change the gtk use-flag to gtk2 and make it possible to activate both, because most people want to set their use-flags globaly like i do. in that case the ebuild should prefer as always the newer gui-toolkit gtk3 use-flag but dont prematurely abort the emerge process!
reassign due to long devaway
That probably does not make sense in this case since gtk+3 support in this package has no future.
Closing as wontfix since 3.10 already removes the GTK+3 support.